1. Field of the Invention
This invention relates generally to position sensors and particularly to position sensors used to detect the relative position of a rotary or linear linkage. More particularly, the invention is for a position sensor for detecting the position of linkages in automobiles and other vehicles.
2. Description of the Related Art
There are a variety of known techniques for sensing position. Optical, electrical, electrostatic, and magnetic fields are all used with apparatus to measure position. A few of the known apparatus are resistive contacting sensors, inductively coupled ratio detectors, variable reluctance devices, capacitively coupled ratio detectors, optical detectors using the Faraday effect, photo-activated ratio detectors, radio-wave directional comparators, and the electrostatic ratio detectors. There are many other known detectors too numerous to mention herein.
The previous detection methods each offer advantages for one or more applications, but none meet all application requirements for all position sensing applications. The limitations may be cost, sensitivity to particular energies and fields, contamination, stability, ruggedness, linearity, precision, or other similar factors which tend to degrade the signal provided or otherwise make the sensor undesirable.
Vehicle applications generally, and automotive applications specifically, are very demanding environments for position sensors. Temperatures may range as high as 150.degree. C. or more. At the other extreme, the sensor may be exposed to extremely cold environments and be expected to function without special preparation or preheating of the position sensors. Additionally, sensors are exposed to harsh road contaminants such as dirt, mud, water, and corrosion-producing elements such as salt. Moreover, vehicle sensors must endure many millions, and perhaps billions, of small motions referred to in the industry as "dithers." The dithers are the result of mechanical motion and vibration transferred from the vehicle to the sensor. Additionally, during the life of a sensor, there may be a million or more full stroke cycles of motion. All of these dithers or movements of the sensor can affect signal quality.
The environments the sensors are exposed to have caused the industry to explore very rugged and durable components for use in such sensors. One particular group of sensors, those which utilize magnetic energy, are rapidly being accepted in these demanding applications. This is because the inherent insensitivity of the magnetic system to contaminants along with the durability of the component makes the system very attractive. The problem with the prior magnetic systems is that they were too expensive to manufacture. Additionally, any lateral movements of the magnets with respect to the detector produced undesirable signal variations.